Metal hydride explosive system

ABSTRACT

A molten metal-liquid explosive device comprising: 
     (1) a metal casing enclosing an inner space; 
     (2) a fusable metal wall dividing the inner space into a liquid chamber and pyrotechnic material chamber; 
     (3) a liquid (e.g., water) contained in the liquid chamber; 
     (4) a pyrotechnic material essentially comprising an intimate mixture of 
     (a) a magnesium nickel alloy hydride of the formula MgNi x  H y  wherein 0&lt;×≦0.50 and 1.50≦y≦2.00 and 
     (b) a oxidizer selected from the group consisting of CuO, Li 2  O 2 , BaO 2 , and mixtures thereof; 
     wherein the molar ratio of oxidizer to magnesium nickel alloy hydride (MgNi x  H y ) is from about 0.75:1 to about (1.50+0.5y):1 and 
     wherein the pyrotechnic material is contained in the pyrotechnic material chamber in an amount sufficient to melt the fusable metal wall dividing the liquid chamber and the pyrotechnic material chamber; and 
     (5) means for igniting the pyrotechnic material.

BACKGROUND OF THE INVENTION

This invention relates to explosive devices and more particularly tosteam or vapor explosive devices.

Conventional chemical explosives are frequently sensitive to heat andimpact. Moreover, they generally yield toxic fumes when they burn as ina fire. Thus, these conventional explosives require special handling andstorage precautions.

A phenomena of considerable industrial importance in recent years andone that may have significant military application is the so calledvapor explosion, often referred to as thermal explosion or steamexplosion. This phenomena results from the extremely rapid heat transferfrom hot liquid (e.g., molten metal) when introduced into cold liquid(e.g., water). Sporadic explosions resulting from this phenomena havebeen responsible for loss of life and property in industry for a numberof years and efforts have been made to understand the extreme violenceof these interactions. It is not presently known exactly how theseexplosions are initiated. However, resultant effects of theseinteractions are drastic, and substantial amounts of energy are releasedduring such explosions.

U.S. Pat. No. 4,280,409, entitled "Molten Metal-Liquid ExplosiveDevice," which issued to Alexander G. Rozner and Horace H. Helms on July28, 1981, discloses an explosive device which comprises

(1) a metal liner composed of a metal selected from the group consistingof aluminum, magnesium, copper, and brass, the liner enclosing achamber;

(2) a liquid contained in the chamber;

(3) a layer of pyrotechnic material surrounding the outside of theliner, the pyrotechnic material composed of a mixture of powders of (a)nickel; (b) metal oxide; and (c) an aluminum containing component whichmay be (i) aluminum or (ii) a mixture of from 50 to less than 100 weightpercent of aluminum and from more than zero to 50 weight percent of ametal which can be magnesium, zirconium, bismuth, beryllium, boron,tantalum, copper, silver, niobium, or mixtures thereof; and

(4) means for igniting the pyrotechnic material. The devices arecompact, self-contained, safe, high energy explosives having relativelyshort initiation to detonation times. Nevertheless the devices work bythe flowing contact of the molten pyrotechnic reaction products and theliquid (e.g., water). It would be desirable to provide a device in whichthe molten pyrotechnic reaction products are propelled into the liquid,thus reducing the initiation to detonation time and increasing theviolence of the explosion. At the same time, it is desirable to retainthe advantages of compactness and safety of the device.

SUMMARY OF THE INVENTION

Accordingly, one object of this invention is to provide a new explosivedevice.

Another object of this invention is to provide an explosive device whichis insensitive to impact, friction, shock and elevated temperature.

Yet another object of this invention is to provide a thermally stableexplosive device which is less likely to detonate in a fire than mostorganic chemical explosives are.

Another object of this invention is to provide an explosive device whichwill not burn or decompose to yield toxic vapors.

A still further object of this invention is to provide a moltenmetal-liquid device in which the molten material is forcefully injectedinto the liquid thus increasing the speed and energy of the resultingexplosion.

These and other objectives of this invention are obtained by providing:

A molten metal-liquid explosive device comprising:

(1) a metal casing enclosing an inner space;

(2) a fusable metal wall dividing the inner space into a liquid chamberand a pyrotechnic material chamber;

(3) a liquid contained in the liquid chamber;

(4) a pyrotechnic material essentially comprising

(a) a magnesium nickel alloy hydride of the formula MgNi_(x) H_(y)wherein 0<x≦0.50 and 1.50≦y≦2.00 and

(b) a oxidizer selected from the group consisting of CuO, Li₂ O₂, BaO₂,and mixtures thereof;

wherein the molar ratio of oxidizer to magnesium nickel alloy hydride(MgNi_(x) H_(y)) is from about 0.75:1 to about (1.50+0.5y):1 and

wherein the pyrotechnic material is contained in the pyrotechnicmaterial chamber in an amount sufficient to melt the fusable metal walldividing the liquid chamber and the pyrotechnic material chamber; and

(5) means for igniting the pyrotechnic material.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily appreciated as the same becomesbetter understood by reference to the following detailed descriptionwhen considered in connection with the accompanying drawings wherein:

FIG. 1 shows a side cross-sectional view of the preferred closed liquidchamber molten metal-liquid explosive device;

FIG. 2 shows a side cross-sectional view of an open liquid chambermolten metal-liquid explosive device; and

FIG. 3 shows a side cross-sectional view of a test molten metalexplosive device used in examples 1 through 4; and

FIG. 4 shows a pressure-time profile of a test (example 1) carried outby using the device shown in FIG. 3;

FIG. 5 shows a side cross-sectional view of the test molten metal-liquidexplosive device used in Example 5; and

FIG. 6 shows a pressure-time profile of a test (example 5) carried outby using the device shown in FIG. 5.

FIGS. 3 through 6 are discussed in detail in the experimental section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein like reference charactersdesignate identical or corresponding parts throughout the severalfigures, and more preferably to FIG. 1 which shows a sidecross-sectional view of the preferred molten metal-liquid explosivedevice which is shown to include a metal outer casing 10 which enclosesa space which is divided by a fusable metal wall 12 into a pyrotechnicchamber 14 and a liquid chamber 16. The liquid chamber 16 contains aliquid 18 (e.g., water) and may have a space 20 to allow for expansionof the liquid 18 upon freezing. The pyrotechnic chamber 14 is lined witha layer of ceramic material 22 which thermally insulates the pyrotechnicchamber 14 and which protects the metal outer casing 10 from erosion.The pyrotechnic chamber 14 is primarily filled with a compacted form ofthe pyrotechnic mixture 24. A portion of the pyrotechnic mixture is inthe form of a powder 26 to facilitate the rapid ignition of thepyrotechnic material 24 and 26. As shown in FIG. 1, an ignition coil 30is inserted into the pyrotechnic material powder 26. The ignition coil30 is attached to electrical leads 28 which pass out through the bolt 32tightened to the outer casing 10 and are attached to a conventionalpower supply not shown.

The device of FIG. 1 operates as follows. An electric current passesthrough the ignition coil 30 igniting the pyrotechnic material power 26which in turn ignites the compacted pyrotechnic material 24. Completionof the reaction takes less than one second. The reaction generates veryhigh (2600° C.) temperatures and produces molten metal material,hydrogen gas, and water vapor. The molten metal material eats away themetal wall 12 and the very high gas pressure resulting from the superheated water vapor and hydrogen gas cause the molten metal material tobe violently ejected from the pyrotechnic material chamber 14 into theliquid 18 in the liquid chamber 16. This extremely quick injection ofmolten material into the relatively cool liquid 18 results in a violentvapor explosion.

FIG. 2 shows a side cross-sectional view of an open liquid chamberdevice which differs from the device shown in FIG. 1 in that no liquidis stored in the liquid chamber 16. Referring to FIG. 2, an opening 34in the outer casing 10 is provided to permit a liquid (e.g., water) toenter the liquid chamber 16 from the external environment (e.g., anocean, river, lake, etc.). The opening 34 may simply be a hole or it maybe a oneway valve or other state of the art device. The remainder of thedevice is as described for FIG. 1. In use the device would be put intothe liquid and the liquid chamber 16 would be allowed to fill with theliquid. The device would then be detonated by igniting the pyrotechnicmaterial.

The pyrotechnic mixture is a critical feature of this invention. Themixture comprises a magnesium nickel alloy hydride as the fuel and anoxidizer selected from the group consisting of copper II oxide (CuO),lithium peroxide (Li₂ O₂), barium peroxide (BaO₂), and mixtures thereof.The mixture not only generates intense heat, but also high pressures dueto low molecular weight gases (e.g., H₂ O, H₂, etc) which forcefullyinject the hot reaction products into the liquid 18 in the liquidchamber 16 after the metal wall 12 has been breached. The magnesiumnickel alloy hydrides are of the type which are used to store hydrogenin hydrogen powered vehicles such as those discussed by J. J. Reilly andGary D. Sandrock in "Hydrogen Storage in Metal Hydrides," ScientificAmerican, (February 1980), Vol. 242, No. 2 pp. 118-129 and by K. C.Hoffman et al. in "Metal Hydride Storage for Mobile and StationaryApplications," International Journal of Hydrogen Energy, Vol. 1, pp.133-151 (Pergamon Press 1976).

The magnesium nickel alloy hydrides may be represented by the generalformula MgNi_(x) H_(y) wherein x is the atomic ratio of nickel tomagnesium and y is the atomic ratio of hydrogen to magnesium. In general0<x≦0.50, preferably 0.05≦x≦0.25, and more preferably 0.10≦x≦0.15, andmost preferably x=2/15; and 1.50≦y≦2.00, preferably 1.80≦y≦2.00, andmore preferably 1.95≦y≦2.00.

Copper (II) oxide (CuO), lithium peroxide (Li₂ O₂), and barium peroxide(BaO₂) are preferred as the oxidizers because they are thermally stableup to 500° C. and their heats of formation (the heat required to releaseoxygen) are lower than the heat of formation of water resulting in a netgain in heat. Copper (II) oxide generates the greatest pressure per unitof volume and lithium peroxide the greatest pressure per unit of weight.Note that nitrate, chlorate, and perchlorate salts are not used in thisinvention as oxidizer salts because of their relative instability.

The reactions between the magnesium nickel alloy hydride and theoxidizers can be represented by the following general equations

    MgNi.sub.x H.sub.y +(1+0.50fy)CuO→MgO+(1+0.50fy)Cu+xNi +0.5(1-f)yH.sub.2 +0.5fyH.sub.2 O                         (1)

    MgNi.sub.x H.sub.y +(1+0.5fy)Li.sub.2 O.sub.2 →MgO+(1+0.5fy)Li.sub.2 O+xNi0.5(1-f)yH.sub.2 +0.5fyH.sub.2 O                     (2)

    MgNi.sub.x H.sub.y +(1+0.5fy)BaO.sub.2 →MgO+(1+0.5fy)BaO+xNi+0.5(1-f)yH.sub.2 +0.5fyH.sub.2 O(3)

wherein f is a fraction ranging from zero to one (0≦f≦1), x is theatomic ratio of nickel to magnesium and y is the atomic ratio ofhydrogen to magnesium in the magnesium nickel alloy hydride. When f iszero, the gas product is mostly hydrogen gas, since magnesium has muchhigher affinity with the oxygen of the oxides. As f approaches one(adding more oxidizer: CuO, Li₂ O₂, or BaO₂) the hydrogen gas reactswith the additional oxidizer exothermically to generate water vapor.Therefore, the pressure generation per unit weight of the reactants ismost efficient when f is zero whereas the heat generation is mostefficient when f is one. Using these equations, the weight of a givenoxidizer per weight of magnesium nickel alloy hydride MgNi_(x) H_(y)needed to produce a stoichiometric reaction mixture can be calculated. Amolar ratio of oxidizer to magnesium nickel alloy hydride of preferablyfrom about 0.75:1.00 to about (1.50+0.5y):1.00, more preferably from1.00:1.00 to (1.00+0.5y):1.00, and most preferably (1.00+0.25 y):1.00 isused wherein y is the atomic ratio of hydrogen to magnesium in themagnesium nickel alloy hydride as shown above.

The pyrotechnic materials used in the molten metal-liquid explosivedevices of this invention can be ignited in various conventional waysand once initiation occurs, the propagation velocity becomes a functionof composition and density among other factors. For example (see FIG.1), compressed powder configurations or pellets 24 made from thepyrotechnic mixtures can be ignited by placing them in contact withloose powders 26 of the same composition and then igniting the powder bymeans a small heating element 30 or alternatively electric matches orconventional ordnance igniter systems.

The final gas pressure depends on the volume ratio of the pellets to thefree inner space of the device. The denser the pellets are and thesmaller volume the free space occupies, the greater the final pressurebecomes. The pressure could be over 40,000 psi.

The metal or alloy used in the metal wall 12 must not melt below theignition temperature of the pyrotechnic mixture but must melt below thetemperature generated by the ignited pyrotechnic mixture. Generally, ametal or alloy melting in the range of from 600° C. to 1400° C. willwork well. Obviously, conventional factors such as strength, cost,corrosion resistance are also taken into consideration. Walls made ofaluminum, copper, magnesium, or brass are preferred with aluminum wallsbeing most preferred.

Referring to FIG. 1, the liquid 18 in the liquid chamber 16 may be wateror any other liquid (e.g., organic solvents, nitric acid, etc.). Wateris the most preferred solvent because it is nontoxic, nonflammable,inexpensive and available. A combination of water and an antifreeze(e.g., ethylene glycol) may be used for low temperature environments. Asshown in FIG. 1, space 20 is left in the liquid chamber 16 for water 18to expand into if it freezes. The amount of liquid used in the preferreddesign (FIG. 1) is from 6 to 15 weight percent of the weight of thepyrotechnic material used. The liquid chamber 16 of the open liquidchambered device (FIG. 2) is also designed to hold 6 to 15 weightpercent of liquid based on the weight of the pyrotechnic material.

In the event of a fire, the liquid must be able to escape from themolten metal-liquid explosive device. Otherwise, an explosion may occur.This may be done by using a rupturable membrane or similar structure. Ametal plug would be screwed into the outer casing over the membraneprior to activation of the molten metal-liquid explosive device. Anotherapproach would be to store the device and liquid separately and thenfill the chamber just prior to use.

The general nature of the invention having been set forth, the followingexamples are presented as specific illustrations thereof. It will beunderstood that the invention is not limited to these specific examples,but is susceptible to various modifications that will be recognized byone of ordinary skill in the art.

EXPERIMENTAL

The magnesium nickel alloy hydride used in Examples 1 through 5 was ofthe formula MgNi₀.133 H₂. The molar ratio of CuO to MgNi₀.133 H₂ used inexamples 1, 2, and 5 was 2:1 (a weight ratio of 160:34). The molar ratioof Li₂ O₂ to MgNi₀.133 H₂ used in examples 3 and 4 was 2:1 (a weightratio of 91:34). Both the pellets and the loose powder in each examplewere of the same composition.

FIG. 3 shows a side cross-sectional view of a device used to test andmeasure the power of the reaction of various magnesium nickel alloyhydride/oxidizer mixtures before the reaction products are mixed withthe liquid (water). This test device was used in Examples 1 through 4.The design of the device is more complex than that of the actualexplosive devices shown in FIGS. 1 and 2 because the test device isdesigned to be reused and to precisely measure the maximum pressuresgenerated by the reactions. (Note that the water chamber is omitted fromthe test device of FIG. 3). Referring to FIG. 3, a hollow cylindricalstainless steel outer casing 10 partially enclose a pyrotechnic chamber14 which is lined with a ceramic liner 22 in combination with a graphiteliner 44. The graphite liner is machined to have a very even surfaceupon which a copper gasket 42 rests. An annular stainless steel lowercap 40 rests on the copper gasket 42. A Holex 1196A igniter 32 isthreaded into the lower cap 40. A cylindrical stainless steel upper cap38 screws into the top of the outer casing 10 and presses down the lowercap 40 which presses the copper gasket 42 against the even surface ofthe graphite liner 44 providing strong air tight seal. A pressuretransducer 46 is screwed into an opening at the bottom of the stainlesssteel outer casing 10 and is used to monitor the pressure inside of thepyrotechnic chamber 14. Magnesium nickel alloy hydride/oxidizer pellets24 are placed in the pyrotechnic chamber 14 and a mixture of loosepowder 26 of the same composition is placed on top of the pellets 24.Leads 28 which pass through a hole 36 in the upper cap 38 connect theHolex igniter 32 and coil 30 to a power supply not shown. The coil 30 isplaced into the loose hydride/oxidizer powder 26. An electric currentpassing through the coil 30 ignites the loose hydride/oxide powder 26which then ignites the hydride/oxide pellets 24. The pressure of theresulting explosive, thermal reaction in the pyrotechnic chamber 14 ismeasured by pressure transducer 46 which is connected to a recordingdevice not shown.

EXAMPLE 1

2 gm of the pellets made of the mixture of the metal hydride and CuO and0.6 gm of the loose powder of the same mixture were ignited. Peakpressure of 2,500 psi was reached in 0.65 second after the ignition(FIG. 4).

EXAMPLE 2

8 gm of the pellets made of the mixture of the metal hydride and CuO and0.6 gm of the loose powder of the same mixture were ignited. Peakpressure of 14,500 psi was reached in 0.2 second after the ignition.

EXAMPLE 3

2 gm of the pellets made of the mixture of the metal hydride and Li₂ O₂and 0.6 gm of the loose powder of the same mixture were ignited. Peakpressure of 9,300 psi was reached in 0.08 second after the ignition.

EXAMPLE 4

4 gm of the pellets made of the mixture of the metal hydride and Li₂ O₂and 0.6 gm of the loose powder of the same mixture were ignited. Peakpressure of 20,000 psi was reached. The reaction was violent enough toblow out the cap.

FIG. 5 shows a side cross-sectional view of a device used to measure themaximum pressure generated by the molten magnesium nickel alloyhydride/oxidizer reaction products with a liquid. The device of FIG. 5is the same as that shown in FIG. 3 except for the followingmodification. The outer casing 10 is extended to accommodate a liquidchamber 16 which is partially filled with water 18 leaving a space 20.The pyrotechnic chamber 14 is separated from the liquid chamber 16 by afusable metal (e.g. aluminum) wall 12. The metal hydride/oxide reactionis initiated as described for FIG. 3 (examples 1-4) above. The resultingmolten reaction products eat through the metal wall 12 and the hydrogengas and water vapor produced by the metal hydride/oxidizer reactioneject the molten reaction products from the pyrotechnic chamber 14 intothe water 18 contained in liquid chamber 16 causing a violent moltenmetal/liquid explosion which is measured by the pressure transducer 46.The transducer 46 is attach to a recording device not shown. The deviceof FIG. 5 was used in example 5.

EXAMPLE 5

8 gm of the pellets made of the metal hydride and CuO and 0.6 gm of theloose powder of the same mixture were ignited and the reaction productswere injected into a 2 ml water pool. Peak pressure of 3,000 psi wasreached with about 0.02 second rise time (FIG. 6). The volume of freespace in this test was considerable larger than the previous tests(examples 1-4).

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims theinvention may be practiced otherwise than as specifically describedherein.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. A molten metal-liquid explosive devicecomprising:(1) a metal casing enclosing an inner space; (2) a fusablemetal wall dividing the inner space into a liquid chamber and apyrotechnic material chamber; (3) a liquid contained in the liquidchamber; (4) a pyrotechnic material essentially comprising(a) amagnesium nickel alloy hydride of the formula MgNi_(x) H_(y) wherein0<x≦0.50 and 1.50≦y≦2.00 and (b) a oxidizer selected from the groupconsisting of CuO, Li₂ O₂, BaO₂, and mixtures thereof; wherein the molarratio of oxidizer to magnesium nickel alloy hydride is from about0.75:1.00 to about (1.50+0.5y):1.00, and wherein the pyrotechnicmaterial is contained in the pyrotechnic material chamber in an amountsufficient to melt the fusable metal wall dividing the liquid chamberand the pyrotechnic material chamber; and (5) means for igniting thepyrotechnic material.
 2. The device of claim 1 wherein 0.05≦x≦0.25. 3.The device of claim 2 wherein 0.10≦x≦0.15.
 4. The device of claim 3wherein x is about 2/15.
 5. The device of claim 1 wherein the liquid isselected from the group consisting of water, liquid aliphatic alcoholsof from 1 to 5 carbon atoms, and mixtures thereof.
 6. The device ofclaim 1 wherein the liquid is water.
 7. The device of claim 1 wherein1.80≦y≦2.00.
 8. The device of claim 7 wherein 1.95≦y≦2.00.
 9. The deviceof claim 1 wherein the molar ratio of oxidizer to magnesium nickel alloyhydride is from 1.00:1.00 to (1.0+0.5y):1.00.
 10. The device of claim 9wherein the molar ratio of oxidizer to magnesium nickel alloy hydride is(1.00+0.25y):1.00.
 11. The device of claim 1 wherein the fusable metalwall is made of a metal selected from the group consisting of aluminum,copper, and magnesium.
 12. The device of claim 11 wherein the fusablemetal is aluminum.
 13. The device of claim 1 wherein the oxidizer isCuO.
 14. The device of claim 1 wherein the oxidizer is Li₂ O₂.
 15. Thedevice of claim 1 wherein the fusable metal wall is made of an alloywhich is brass.